attiny13aでPB2につけた可変抵抗をadcしてPB1につけたLEDをPWMする

 // https://adnbr.co.uk/articles/adc-and-pwm-basics

/* ---------------------------------------------------------------------

 * PWM LED Brightness control for ATtiny13.

 * Datasheet for ATtiny13: http://www.atmel.com/images/doc2535.pdf

 *

 * Pin configuration -

 * PB1/OC0B: LED output (Pin 6)

 * PB2/ADC1: Potentiometer input (Pin 7)

 *

 * ~100 bytes.

 *

 * Find out more: http://bit.ly/1eBhqHc

 * -------------------------------------------------------------------*/

// 9.6 MHz, built in resonator

#define F_CPU 9600000

#define LED PB1

#include <avr/io.h>

 

void adc_setup (void)

{

    // Set the ADC input to PB2/ADC1

    // admux https://garretlab.web.fc2.com/arduino/inside/hardware/arduino/avr/cores/arduino/wiring_analog.c/analogRead.html

    ADMUX |= (1 << MUX0); // analog pin select // ADC1 i.e. PB2

    ADMUX |= (1 << ADLAR); // 左詰めで結果をいれる？

 

    // Set the prescaler to clock/128 & enable ADC

    // At 9.6 MHz this is 75 kHz.

    // See ATtiny13 datasheet, Table 14.4.

    // ADEN::ADC-OK, ADPS1 AND ADPS0 TO 1/8 ? (1<<ADPS2) | が抜けている？

    ADCSRA |= (1 << ADPS1) | (1 << ADPS0) | (1 << ADEN);

}

 

int adc_read (void)

{

    // https://awawa.hariko.com/chira-ura/atmega168-chapter23-jp.html

    // Start the conversion

    ADCSRA |= (1 << ADSC); // ADC START CONVERSION

    // Wait for it to finish

    while (ADCSRA & (1 << ADSC));  // 読み取りおわったらADCSRAはゼロとなる？

    return ADCH; // 上位８ビットのみ返す

}

 

void pwm_setup (void)

{ // https://usicolog.nomaki.jp/engineering/avr/avrPWM.html

    // Set Timer 0 prescaler to clock/8.

    // At 9.6 MHz this is 1.2 MHz.

    // See ATtiny13 datasheet, Table 11.9.

    TCCR0B |= (1 << CS01); // prescale 1/8

    // Set to 'Fast PWM' mode

    TCCR0A |= (1 << WGM01) | (1 << WGM00);

    // Clear OC0B output on compare match, upwards counting.

    TCCR0A |= (1 << COM0B1);

}

 

void pwm_write (int val)

{

    OCR0B = val;

}

 

int main (void)

{

    int adc_in;

 

    // LED is an output.

    DDRB |= (1 << LED);  

 

    adc_setup();

    pwm_setup();

 

    while (1) {

        // Get the ADC value

        adc_in = adc_read();

        // Now write it to the PWM counter

        pwm_write(adc_in);

    }

}